KR100464309B1 - Micro-accelerometer for detecting acceleration and manufacturing method thereof - Google Patents

Abstract

The present invention describes a microaccelerometer for detecting an inertial acceleration of an object and a manufacturing method thereof. Micro accelerometer according to the present invention is an inertial mass arranged to vibrate in a vertical direction to the substrate by floating at a position spaced apart from the substrate at a predetermined interval to detect the acceleration in the vertical direction; At least one elastic member connected to the inertial mass to support a distance from the substrate to enable vibration in the vertical direction; An anchor fixed to the substrate to support the elastic member; Moving combs connected to intersect the elastic member to provide electrostatic force in a direction perpendicular to the elastic member and the inertial mass; Fixed combs arranged side by side while maintaining a constant distance between the moving comb; And a support formed on the substrate to fix the fixed combs; and detecting an acceleration by changing a capacitance change according to a change in the overlapping area of the fixed comb and the moving comb into an electrical signal with respect to the input acceleration. .

Description

Area-changing capacitive microaccelerometer and manufacturing method {Micro-accelerometer for detecting acceleration and manufacturing method}

The present invention relates to a micro-accelerometer for detecting an inertial acceleration of an object and a method of manufacturing the same. Specifically, at least one moving comb arranged to form a part of an inertial mass plate during vertical acceleration input. The present invention relates to a micro accelerometer for detecting a change in capacitance caused by a change in area between an electrode and a fixed comb electrode fixed to a substrate, and a manufacturing method thereof.

Recently, with the development of semiconductor process technology, the development of inertial sensors using Micro Electro Mechanical System technology has been actively conducted. In particular, silicon accelerometers are structurally using a conventional pendulum accelerometer. In terms of process methods, bulk micromachining, surface micromachining, or bulk-surface micromachining mixing techniques were employed. In bulk micromachining, an accelerometer having good characteristics can be manufactured by using a silicon single crystal having excellent mechanical and thermal characteristics.

Micro accelerometers are applied to autonomous navigation systems, suspensions, airbag systems in automobiles, and their application ranges such as physical quantity measurement such as vibration, tilt and shock are expanding. In recent years, in order to meet the trend of miniaturization, light weight, and low price of such a system, there has been a rapid increase in researches in which sensors are manufactured in a semiconductor process. Recently, analog devices in the US, Motorola, Bosch in Germany and Hitachi in Japan have already developed and released microaccelerometers using silicon processes.

As an example of a micro accelerometer for sensing acceleration in the vertical direction

Hitachi's capacitance type accelerometer (US Pat. No. 5,350,189) is shown in FIG. As shown, the capacitive accelerometer has a structure in which the insulating substrates 1 and 3 and the silicon substrate 2 are integrated. The fixed electrodes 5 and 6 are formed inside the insulating substrates 1 and 3 by sputtering, and the insulating substrates 1 and 3 and the silicon substrate 2 are bonded by anodic bonding. It is structured. The moving electrode 4 is horizontally connected to the silicon substrate 2 by a cantilever for supporting the moving electrode 4. The surface of the moving electrode 4 is formed with an electrode to detect the acceleration in the vertical direction with respect to the plane of the moving electrode 4, and a plurality of grooves 7 are dug to reduce air damping. When the acceleration in the vertical direction is input to the capacitive accelerometer, it is placed in the direction opposite to the acceleration in the vertical direction input by the inertia caused by the vibration of the moving electrode 4, and the distance between the fixed electrode and the moving electrode is changed. This results in a change in capacity. Acceleration can be detected by measuring this change in capacitance with an electrical signal. The capacitive accelerometer measures the change in capacitance due to the change in the distance between the fixed electrode and the moving electrode, but the acceleration measurement range is limited because the change in distance and the change in capacitance are nonlinear. The V-groove was cut to reduce air resistance. This method can increase the surface area of the moving electrode 4 and at the same time control the flow of air to some extent. However, the moving electrode 4 and the upper and lower fixed electrodes have high sensitivity and large bandwidth in terms of design and process. There is a limiting factor in determining the spacing between (5,6).

2 is a cross-sectional view of a micro mechanical accelerometer described in US Pat. No. 5,504,032. As shown, the micromechanical accelerometer has a structure in which five semiconductor wafers 1, 2, 3, 4, and 5 are insulated from each other by a thin semiconductor oxide film. The micromechanical accelerometer forms a differential capacitor through a signal processor forming a closed loop with upper and lower countereletrodes 6,7 through contact windows 10 and 11. When the acceleration in the vertical direction is input to the plane of the movable mass (movabal mass. 14) connected to the central frame (16) by the web (webs. 15), the movable mass 14 pendulum moves up and down. Will be At this time, a change in distance between the mobile mes 14 and the up and down opposite electrodes 6 and 7 occurs and the acceleration is sensed by converting the change in capacitance due to the distance into an electrical signal and measuring it through the signal processor. can do. This micromechanical accelerometer has a disadvantage in that the acceleration measurement range is limited because the change value of the capacitor and the change value of the distance are nonlinear, and also several times to form the movable scalpel 14 and the up and down counter electrodes 6 and 7. Wafer micromachining process is required, and the process process is complicated, process cost is high, such as several wafer bonding to combine each component, and the area of the mobile scalpel 14 is required to obtain high sensitivity. It should be large and the distance between the moving mes 14 and the up and down counter electrodes 6 and 7 should be very small, but the small distance between the moving mes 14 and the moving mes 14 and the up and down opposite electrodes 6 and 7 There is a problem that acts as a limiting factor to reduce the bandwidth of the accelerometer by increasing the air resistance.

The present invention has been devised to improve the above problems, using a silicon on insulator (SOI) wafer to simplify the manufacturing process as much as possible, and to reduce the air resistance by having a plurality of holes penetrating up and down in the mass portion; It is an object of the present invention to provide an area change capacitive micro accelerometer and a method of manufacturing the same, which can increase the sensitivity while detecting a change in capacitance caused by an area change.

Area change capacitive micro-accelerometer according to the present invention to achieve the above object, the substrate; An inertial mass arranged to oscillate in a direction perpendicular to the substrate by floating at a position spaced apart from the substrate at a predetermined interval so as to sense acceleration in a vertical direction; At least one elastic member connected to the inertial mass to support a distance from the substrate to enable vibration in the vertical direction; An anchor fixed to the substrate to support the elastic member; Moving combs connected to intersect the elastic member to provide electrostatic force in a direction perpendicular to the elastic member and an inertial mass; Fixed combs arranged side by side while maintaining a constant gap between the moving combs; And a support formed on the substrate to fix the fixing combs.

In the present invention, the inertial mass is formed in a polygonal or circular shape, the elastic member and the moving comb and the fixed comb is preferably formed in a rotationally symmetrical form.

In addition, in the present invention, the moving comb and the fixed comb is formed with a predetermined thickness difference in order to detect the acceleration of vertical up and down vertically, in the vertical direction of the moving comb to the fixed comb when no voltage is applied It is preferable to arrange the position of differently.

In addition, in order to achieve the above object, the manufacturing method of the area-change capacitance type micro accelerometer according to the present invention comprises the steps of: (a) depositing a silicon layer for forming an inertial mass and a metal layer for wiring on a substrate on which a sacrificial layer is formed; ; (B) patterning the metal layer to form a wiring pattern; (C) selectively etching the inertial mass forming silicon layer to form an inertial mass, a moving comb, a fixed comb, and an elastic member; And (d) removing all the sacrificial layers except the sacrificial layer below the wiring pattern to separate the inertial mass, the moving comb, and the elastic member from the substrate.

In the present invention, the wiring metal layer in the step (a) is formed of Au / Cr, the step (b) is a dry etching method of the deposited metal layer through a photolithography process, the (c) In the step, the dry etching process using the photolithography method is preferably performed twice so that the movable comb and the fixed comb have a predetermined thickness difference.

Hereinafter, an area-change capacitance type micro accelerometer and a manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

The microaccelerometer of the present invention is an integrated microaccelerometer having a displacement detection unit circuit for outputting the displacement generation of the inertial mass and the inertial mass due to the applied acceleration, shock, or vibration as an electrical signal. An acceleration is detected by changing a change in capacitance according to a change of the overlapped area of the fixed comb and the moving comb into an electrical signal.

3 is a detailed view of the displacement generating part of the inertial mass, the inertia mass 11, the spring 10, the support 13, and the moving comb 5 formed in the shape of a comb in parallel with the spring 20 connected to the spring 20; 8), the fixed comb (6,7), the spring (10) and the inertial mass (11) connected to the support 13 and formed in the shape of a comb in parallel with the movable comb (5,8) substrate 20 It is composed of anchors (3) for fixing to. Dozens of holes 12 are drilled in the inertial mass 11 to reduce air resistance. Anchors (3) for fixing the inertial mass (11), moving combs (5,8), fixed combs (6,7), spring (10) to the substrate (20) and pads (1,2) for electrical contact Is sufficiently large so that the sacrificial layer 21 is not etched and fixed to the substrate 20. Except for the pads for anchors and electrical contacts, all structures (5,6,7,8,9,10) are in the form of floating in the air, and are symmetrical with respect to AA 'and BB'. It is.

FIG. 4 is formed by arranging pads and anchors in a circle around the inertial mass, and the operating principle thereof is the same as the description of the structure shown in FIG.

As shown in FIG. 5, the moving comb 5 and the fixed comb 6 located in the y-axis direction form the capacitor C1, and the moving comb 8 and the fixed comb 7 located in the x-axis direction form the capacitor C2. Form. And C1 and C2 form an array of differential capacitors. The moving comb 5 and 8 and the fixed comb 6 and 7 form a differential capacitor C1 and C2 as shown in FIG. 4, and if there is no acceleration input from the outside, the differential capacitors C1 and C2 have the same value as shown in FIG. 4. Keep it.

In this configuration, when there is an acceleration input from the outside, the principle of detecting the acceleration will be described with reference to FIG. 6.

As shown in FIG. 6, when acceleration is applied from the outside in the + Z axis direction, the moving comb teeth 5 and 8 move in the -Z axis direction, thereby reducing the overlapped area of the moving comb 8 and the fixed comb 7, thereby decreasing C2. And, since the overlapped area of the moving comb 5 and the fixed comb 6 does not change, C1 does not change. In addition, as shown in FIG. 7, when acceleration is applied from the outside in the -Z axis direction, the moving comb teeth 5 and 8 move in the + Z axis direction, so that the overlapped area of the moving comb 5 and the fixed comb 6 is reduced, and thus C1 is Since the overlapped area of the moving comb 8 and the fixed comb 7 does not change, C 2 does not change. At this time, the difference (C1-C2) between the values of the two capacitors generated by the acceleration is converted into an electrical signal in the configuration as shown in FIG. That is, AC voltage sources 30 and 31 having the same voltage value and opposite signs but opposite frequency and amplitude but opposite phases have moving combs 5 and 8 and fixed combs 6 and 7 as shown in FIG. In this case, the two power supplies 30 and 31 drive the differential capacitors C1 and C2, respectively. The displacement d in the Z direction of the inertial mass 11 and the moving comb 5 and 8 occurs with respect to the applied acceleration, and as a result, the magnitude of the signal at point a is the difference between the values of the two capacitors C1 and C2. Equal to (C1-C2), the value of which is proportional to the magnitude of the applied acceleration. In addition, the phase at point a indicates the direction in which the acceleration is applied. Here, the charge amplifier 32 is used as a converter for converting the difference between the two capacitances into an electrical signal. The arrangement of the differential capacitors can be effectively eliminated by differentially affecting external influences such as temperature and electrical noise. Here, the output through the charge amplifier is an AC voltage signal, and the output is converted into direct current through the demodulator 33 and the low pass filter 34.

On the other hand, the manufacturing method of the area-change capacitive micro-accelerometer of the above structure is as follows.

That is, first, as shown in FIG. 9A, a metal layer (Au / Cr) 22 and a photoresist layer are sequentially deposited on an SOI wafer composed of silicon 20 / silicon oxide film 21 / silicon 23. The mask 24 is formed through a photolithography process.

Next, as shown in FIG. 9B, the metal layer 22 is etched to form the wiring metal 22.

Next, as shown in FIG. 9C, the silicon film 23 is etched by the step t between the fixed comb and the moving comb by using a photolithography process on the silicon film 23. Reference numeral 25 is a photoresist pattern.

Next, as shown in FIGS. 9D to 9E, a photoresist pattern 26 is formed on the etched silicon film 23 to distinguish between C1 and C2, and the photoresist pattern 25 previously formed is formed together with the photoresist pattern 25. The silicon film 23 is etched to form the moving combs 5 and 8 and the fixed combs 6 and 7.

Next, as shown in FIG. 9F, the photoresist patterns 25 and 26 are removed and the sacrificial layer 21 is etched away so that the structures float in the air over the substrate 20. In this manner, the fixed comb teeth and the moving comb teeth having the thickness difference t are formed.

Here, the silicon film 23 (see FIG. 9A) for forming structures such as the mass body 11, the moving comb teeth 5 and 8, the fixed comb teeth 6 and 7, the spring 10, and the like has a high resistivity, and has a low resistivity. The thickness is several tens of micrometers. A metal (Au / Cr) 22 is deposited on the SOI wafer, and the upper silicon film 23 is subjected to two photolithography processes and silicon dry etching. The mass 11, the moving combs 5 and 8, and the fixed comb 6, 7), the spring 10 to form a structure. That is, as shown in FIGS. 5 and 9, in order to distinguish between C1 and C2, a thickness difference t is formed through two photolithography processes and silicon dry etching to complete a highly sensitive area change capacitive microaccelerometer.

As described above, the area-change capacitive microaccelerometer according to the present invention is manufactured as an integrated body using an SOI wafer, so that an electrostatic accelerometer can be manufactured in a very simple process requiring no three separate masks and only three masks.

As described above, the present invention reduces the process steps by using a silicon on insulator (SOI) wafer, reduces the air resistance, and can produce an area-change capacitive microaccelerometer with high sensitivity. This micro accelerometer has a linear relationship between input and output because the area change capacitance is the basic configuration, and all the components such as inertial mass, spring, capacitor, and comb are processed from the same layer, so the process is simple. It greatly improves the noise ratio and increases the sensitivity by arranging several differential capacitors. In addition, two silicon etching processes from the same silicon layer were used to construct a differential capacitor. In this way, this structure is a simple process, it is possible to manufacture a single-axis vertical bidirectional accelerometer with high sensitivity, wide bandwidth, low signal-to-noise ratio.

1 is a perspective plan view of a conventional micro accelerometer,

2 is a perspective plan view of a conventional micro accelerometer,

3 is a perspective plan view of an area change capacitance type micro accelerometer according to the present invention;

Figure 4 is another embodiment of the area change capacitance type micro accelerometer according to the present invention,

5 is a vertical cross-sectional view of an area change capacitance type micro accelerometer according to the present invention;

6 is an operation principle diagram of the area change capacitive micro accelerometer according to the present invention when the acceleration is input in the + Z direction.

7 is an operation principle of the area-change capacitance type micro accelerometer according to the present invention when the acceleration input in the -Z direction,

8 is a conceptual diagram showing the displacement detection principle of the displacement generating portion of the mass inertia of the area change capacitance type microaccelerometer according to the present invention;

9A to 9F are vertical cross-sectional views after each step of manufacturing the area change capacitive microaccelerometer according to the present invention.

<Description of the symbols for the main parts of the drawings>

1,2. Pad 3. anchor

5,8. Move comb 6,7. Fixed comb

10. Spring 11. Inertial Mass

12. Hole 13. Support

20. Substrate 21. Sacrificial Layer

Claims (8)

 Board; An inertial mass having a plurality of perforated holes arranged in a position spaced apart from the substrate at a predetermined interval to sense acceleration in a vertical direction and vibrating in a vertical direction to the substrate, and having a plurality of perforated holes for reducing air resistance during vertical vibration; At least one elastic member connected to the inertial mass to support a distance from the substrate to enable vibration in the vertical direction; An anchor fixed to the substrate to support the elastic member; Moving combs connected to intersect the elastic member to provide electrostatic force in a direction perpendicular to the elastic member and an inertial mass; Fixed combs arranged side by side while maintaining a constant gap between the moving combs; And A supporter formed on the substrate to fix the fixing combs; And the mutually opposite area between the moving combs and the fixed comb is changed by the vertical vibration of the inertial mass. The method of claim 1, The inertial mass is an area-change capacitance type micro acceleration sensor, characterized in that formed in a polygon or a circle. The method according to claim 1 or 2, And the elastic member, the moving combs and the fixed combs are formed rotationally symmetrically. The method of claim 1, The moving comb and the fixed comb are formed with a predetermined thickness difference in order to sense the acceleration of the vertical up and down, but when the voltage is not applied to arrange the position of the moving comb in the vertical direction to the fixed comb differently Area-change capacitive micro acceleration sensor. (A) sequentially depositing a silicon layer for forming an inertial mass and a metal layer for wiring on a substrate on which a sacrificial layer is formed; (B) patterning the metal layer to form a wiring pattern; (C) selectively etching the inertial mass forming silicon layer to form an inertial mass, a moving comb, a fixed comb, and an elastic member; And (D) removing the sacrificial layer except the sacrificial layer below the wiring pattern to separate the inertial mass, the moving comb and the elastic member from the substrate; Manufacturing method. The method of claim 5, The wiring metal layer in the step (a) is a manufacturing method of the area-change capacitance type micro acceleration sensor, characterized in that formed of Au / Cr. The method of claim 5, The step (b) is a method of manufacturing a capacitive micro-acceleration sensor, characterized in that by the dry etching method of the deposited metal layer through a photolithography process. The method of claim 5, In the step (c), the dry etching process using the photolithography method is performed twice so that the movable comb and the fixed comb have a predetermined thickness difference.